Setting The setting was secondary care. The economic study was carried out in Hong Kong.

Transcription

1 The diagnostic value and cost-effectiveness of creatine kinase-mb, myoglobin and cardiac troponin-t for patients with chest pain in emergency department observation ward Choi Y F, Wong T W, Lau C C Record Status This is a critical abstract of an economic evaluation that meets the criteria for inclusion on NHS EED. Each abstract contains a brief summary of the methods, the results and conclusions followed by a detailed critical assessment on the reliability of the study and the conclusions drawn. Health technology The authors studied three cardiac markers in patients presenting with chest pain of suspected cardiac origin. The markers were creatine kinase MB isomer (CKMB), myoglobin and cardiac troponin-t. Type of intervention Diagnosis. Economic study type Cost-effectiveness analysis. Study population The study population comprised patients aged above 30 years with chest pain, or chest discomfort, of suspected cardiac origin and of recent onset (within one week). Patients whose electrocardiogram suggested AMI, or those who had a clinical diagnosis of acute coronary syndrome or unstable angina, were excluded. Further exclusion criteria were AMI or cardiac catheterisation within the past month, discharge against medical advice, and chest pain suspected to be of nonischaemic origin. Setting The setting was secondary care. The economic study was carried out in Hong Kong. Dates to which data relate The dates when the effectiveness and cost data were collected were not reported. The price year was likely to have been Source of effectiveness data The effectiveness data were derived from a single study. Link between effectiveness and cost data The costing was carried out prospectively on the same sample of patients as that used in the effectiveness study. Study sample The authors did not report that power calculations were used to influence the number of participants and so estimate the influence of chance on the results. The study incorporated all patients entering the study setting and adhering to the inclusion criteria. The sample was appropriate for the clinical question as it included patients who might have required treatment with the technologies of interest. From the 498 study forms completed, 18 were excluded leaving 480 valid Page: 1 / 5

2 cases. Reasons for exclusions were missing patient identity label on the study form (16 cases), age younger than 30 (1 case), and percutaneous transluminal coronary angioplasty performed two weeks prior (1 case). Study design The analysis was based on both a diagnostic accuracy study and a prospective case series study over a period of up to 6 months. This study was conducted in a single centre. Data were collected by the attending doctors who completed a specially designed form, and accuracy was verified through cross-checking with patient records. Although not clearly stated by the authors, the 'gold' standard when assessing diagnostic accuracy appears to have been the final diagnosis made by the medical department. At 30 days, 5 (1%) patients were lost to follow-up. The patients were followed for a variable period up to 6 months after leaving the observation ward. Analysis of effectiveness The primary health outcomes were: the prevalence of AMI, survival at 7 and 30 days after discharge from the observation ward, and the diagnostic accuracy of the technologies (sensitivity, specificity, positive predictive value, negative predictive value, and likelihood ratios for a positive test and a negative test). The authors did not report any summary statistics for the study participants. Effectiveness results According to the final diagnoses, 7 cases (1.5%) were of proven AMI. No one died within 7 days, although one person died of terminal malignancy within 30 days. Sensitivity was 0.57 for CKMB, 0.29 for myoglobin and 1 for troponin-t. Specificity was 0.94 for CKMB, 0.89 for myoglobin and 0.99 for troponin-t. The positive predictive value was 0.13 for CKMB, 0.04 for myoglobin and 0.70 for troponin-t. The negative predictive value was 0.99 for CKMB, 0.99 for myoglobin and 1 for troponin-t. The likelihood ratio for a positive test was 9.5 for CKMB, 2.6 for myoglobin and 100 for troponin-t. The likelihood ratio for a negative test was 0.46 for CKMB, 0.8 for myoglobin and 0 for troponin-t. Clinical conclusions The authors concluded that the diagnostic performance of troponin-t was much better than CKMB, and that myoglobin is of no value on account of its lack of specificity. Measure of benefits used in the economic analysis The authors did not estimate a summary measure of health benefits. In effect, a cost-consequences analysis was performed. Direct costs Few details of the costing analysis were reported. In particular, the authors did not report the perspective from which Page: 2 / 5

3 the costing was carried out. The authors reported that the cost of reagents for measuring CK, CKMB, myoglobin and troponin was obtained from the biochemistry laboratory in the study setting. The analysis appears to have focused on the immediate direct costs of diagnosing patients and the cost-savings due to unnecessary admissions avoided. The unit costs were reported separately from the resource quantities. Discounting was not reported, but it would not have been relevant if the authors were interested only in the immediate diagnostic costs. One-day admission costs to the study setting were reported for 2002, but it was unclear whether this was also the price year for the entire study. Statistical analysis of costs The costs were treated deterministically. Indirect Costs The indirect costs were not included in the study. Currency Hong Kong dollars (HK$). Sensitivity analysis There was no report of sensitivity analyses being carried out. Estimated benefits used in the economic analysis See the 'Effectiveness Results' section. Cost results The cost of reagents for CK or CKMB measurement was HK$1,259. The total cost (for all patients) of troponin-t measurement was HK$25,440. The incremental cost of troponin-t over CK or CKMB was HK$24,181 (a 20-fold increase). Troponin-T would have saved 24 unnecessary admissions of 2 days each if used instead of CKMB (false-positive with CKMB), resulting in a saving of HK$141,984. Troponin-T would have saved 3 unnecessary admissions of 6 days each if used instead of CKMB (false-negative with CKMB), resulting in a saving of HK$53,244. The total cost-saving of using troponin-t was HK$171,047. Synthesis of costs and benefits The costs and benefits were not combined. Authors' conclusions Troponin is more accurate in diagnosing acute myocardial infarction (AMI) or acute coronary syndrome (ACS) than creatine kinase MB isomer (CKMB), but it is much more expensive. However, the reduction in unnecessary admissions makes troponin highly cost-effective. CRD COMMENTARY - Selection of comparators Page: 3 / 5

4 The authors compared CKMB, myoglobin and cardiac troponin-t as alternatives for diagnosing chest pain. CKMB was reported as being a conventional marker, with myoglobin and cardiac troponins being newer alternatives. You should decide if the comparator represents the current practice in your own setting. Validity of estimate of measure of effectiveness The analysis was based principally on a diagnostic study with an element of a prospective case series study. The design was appropriate to address the study question of the diagnostic value of the health technologies. Further details of the study sample, such as demographics, might have been given to set the context for the reader and enable an assessment of generalisability to other settings. Although the authors reported appropriate outcomes for a diagnostic study, they did not state which health technology was used as the 'gold' standard against which to assess all other technologies. Validity of estimate of measure of benefit The authors did not derive a summary measure of health benefit. The analysis was, in effect, a cost-consequences study. Validity of estimate of costs Although the perspective for the costing analysis was not reported, the costs that were estimated seem to indicate that the perspective of the health care provider was adopted, in this case the hospital. The authors focused on the immediate cost associated with using the diagnostic techniques, and compared the relative cost and cost-saving of each technology. The costs of the reagents were reported separately, which will enhance the generalisability of the results to other settings. It was unclear whether overhead costs were incorporated in the unit cost estimates. One source of the costs was reported, and no other source was used. No statistical or sensitivity analysis of the costs was carried out, which limits the interpretation of the results. The price year was partially reported, but there is doubt about whether this was the price year for the entire study. This may hinder reflation exercises in other settings. Discounting was not relevant and was appropriately not carried out. Other issues The authors discussed the diagnostic performance results. They drew comparisons with other studies and their own prior expectations, drawing on factors such as the incidence of AMI in their own setting to explain some of the results. The issue of generalisability to other settings was not addressed, but it is likely that it will be quite low due to the institution-specific costs used and the lack of statistical and sensitivity analyses to explore the robustness of the results. Several limitations were presented. These centred on the cost-effectiveness being an over-simplified estimate due to, amongst other reasons, not including indirect costs to the individual and society, not including the costs of mortality and morbidity, and not accounting for longer run costs. The authors reported that the limitations led to an underestimate of the cost-effectiveness of troponin. Implications of the study The authors recommended that troponin replace CKMB for the diagnostic evaluation of chest pain patients in the observation ward. They also recommended against the use of myoglobin in the emergency department observation ward. There were no suggestions for further work. Source of funding None stated. Bibliographic details Choi Y F, Wong T W, Lau C C. The diagnostic value and cost-effectiveness of creatine kinase-mb, myoglobin and cardiac troponin-t for patients with chest pain in emergency department observation ward. Hong Kong Journal of Emergency Medicine 2004; 11(2): Page: 4 / 5

5 Powered by TCPDF ( Indexing Status Subject indexing assigned by CRD MeSH Angina Pectoris /diagnosis /economics; Chest Pain; Clinical Trials as Topic; Costs and Cost Analysis; Creatine Kinase /diagnostic use /economics; Emergency Service, Hospital; Heart Diseases /diagnosis; Hospitalization; Myoglobin /diagnostic use /economics; Patient Admission; Prospective Studies; Sensitivity and Specificity; Troponin T /diagnostic use /economics AccessionNumber Date bibliographic record published 31/08/2005 Date abstract record published 31/08/2005 Page: 5 / 5